The present invention concerns the packaging technology of flexible containers, particularly those provided with a zipper-stripe working as the opening and closing device for the packages.
A number of related patents have been issued in this particular field, including European Patent Nos. 0223125, 0276554, 0302144, 0319995,0339324, 0423456, 0528721, International Application No. WO 91/17086, and U.S. Pat. Nos. 4,756,629, 4,876,842, and 5,024,537.
From the evaluation of the patent literature listed above, one will gather the problems of transversal sealing of containers inside which a zipper-stripe is attached. In fact, the zipper-stripe causes problems for proper performance of the sealing operation upon transverse sealing of the package.
European Patent No. 0667228 illustrates a machine that copes with the mentioned problem by cutting a small stripe of the closed zipper before sealing it onto the inside walls of the container in the packaging process. The former procedure, however, does not ensure that the portion of zipper is applied to the inner sides of the container in such a position that it will not interfere with the side sealing zones that work as flanks for the container. This invention also employs a device that adjusts and verifies the position of the zipper portion as related to the subsequent transversal sealings. Furthermore, the zipper portion, after being cut in a continuous stripe, is abandoned and advances only by adhering to the inner sides of the flexible material film.
It is an object of the present invention to provide a new and improved method for ensuring exact positioning of a zipper-stripe in a container during manufacture so as to not have it interfere with the transverse sealing zones that will eventually provide the flanks of the completed containers.
According to the present invention, a method of applying a portion of a closed zipper inside a container of flexible material during manufacture of the container is provided, which comprises the steps of:
applying a length of a closed zipper to the inner side of a film of flexible material with a fixing device in such a position that it will not interfere with transverse sealing zones of a container to be formed from the flexible material; and
cutting the zipper to a portion of length less than the inner width of the container after the the zipper has been applied to the inner side of the film with the fixing device.
This method solves the problem of the prior art procedures in a simple and reliable fashion, since a zipper-stripe or portion is applied to the inner side of the film of flexible material before being cut into portions of smaller length than the inner width of the container, thus avoiding the risk of the zipper extending into the transverse sealing zones and making positioning of the zipper easier, since it is not cut until it has been applied and secured to the container.